The blooming of silicone rubber products is caused by a variety of reasons. For silicone rubber products that have bloomed, only by analyzing the cause of blooming can they be effectively dealt with.
Causes and preventive measures:
1. Visually, once the finished rubber is sprayed with frost, there will be traces on the surface of the product (that is, the sprayed small molecular agglomerates).
2. It is easy to identify the blooming caused by the lack of sulfur in the product, because this blooming is often local and accidental. This can be solved by improving the vulcanization process or strengthening the formula vulcanization system.
3. Frost spray caused by improper storage conditions is also easy to identify, as long as different comparison tests are carried out on storage temperature, time, humidity, etc., it can be identified. This can be avoided as long as proper storage conditions are adopted.
4. It is also easy to identify the blooming caused by the fluctuation of the quality of the raw materials, because this blooming is usually accidental and in batches. In this regard, it can be identified as long as the comparison test is carried out on different batches and different origins of the raw materials. In this way, as long as the batches and origins of raw materials are adjusted, it can be solved.
5. The frost spray caused by improper process operation is also easy to identify, because this kind of frost spray is accidental and local. In this regard, as long as the compounding agent is accurately weighed, mismatching, over-mixing, under-mixing, and missing mixing are avoided, and the operation is strictly carried out according to the process, so as to avoid uneven mixing of the rubber compound and excessively high roller temperature, it can be solved.
6. The frosting caused by the aging of rubber can be identified according to its characteristics that it is easy to occur in the summer with high temperature and in the environment of sun exposure. It is difficult to identify the bloom caused by the excessive use of the compounding agent, and the one-to-one exclusion method can only be used for this. The above two kinds of frosting are in large quantities, and the consequences are relatively serious, and it is relatively difficult to deal with. Generally, wipe the frosting material, soak it in solvent for 4 to 6 hours, take it out to dry in the shade, and pack it into a bag. But to fundamentally solve it, it is necessary to improve the compound formula.
Bloating can only be solved by improving the mixing uniformity of the rubber compound and adjusting the formula
Sulfur is added last when NR is re-mixed. Sulfur used in NBR is often added at the beginning of mixing, and the accelerator is added last. The main reasons for blooming are solubility and the compatibility of sulfur in the rubber compound. Therefore, controlling the content of soluble sulfur in insoluble sulfur is the key to overcoming blooming, and the transformation of insoluble sulfur is related to time and temperature.

The probability of frost spraying in summer is greater than that in winter. It is analyzed that summer is hot, air humidity is high, process temperature control is difficult, and the rubber compound is not cooled well, which prolongs the heating process and causes more insoluble sulfur to be converted into soluble sulfur; summer; When the ambient temperature is high, the temperature is used to control the rubber material to discharge the rubber. When the temperature reaches the same temperature, the mixing time is shortened, the rubber material is not fully mixed, and the sulfur dispersion is poor, which reduces the compatibility of the sulfur and the rubber material; high humidity also accelerates frost spraying.

On the other hand, from the perspective of molecular kinematics, high temperature increases the kinetic energy of sulfur molecules, and it is also easy for sulfur to migrate to the rubber surface. Blooming is also prone to occur when the content of small molecular compounds in the rubber compound is high. Tests have shown that PVC film is beneficial to reduce blooming, and has a great effect on protecting the surface cleanliness and adhesion of the cord. In addition, the rubber must be fully kneaded, and the kneading time can be extended without scorching, which can reduce the content of small molecules and substances in the rubber.

Blooming phenomenon is a common problem in rubber, and the reason is mainly determined by the solubility and dosage of various compounding agents in rubber. When the dosage exceeds its solubility in the rubber, it will migrate from the inside of the rubber material to the surface of the rubber material after a short period of time, which is the usual blooming. There are many materials that may cause blooming, and there are many factors that affect the ship. For example, some are affected by the pH of the material; some are related to the movement activity of the material; some are related to the material processing technology and so on.
In summary, there are a few things:
1) The formula designer considers the solubility of various materials in the rubber compound, and also considers the interaction of various materials in the entire rubber compound system, whether new materials will appear, and whether the emergence of such materials will cause blooming ;
2) Matters needing attention in the process of rubber compound processing, for example, when mixing, the temperature should not be too high when adding vulcanizing agent, the reason is just like what the boss said.
3) The storage conditions of the finished rubber compound must be suitable for the storage conditions, temperature, humidity, etc. of the rubber;
4) The post-vulcanization of the product must be sufficient, and the crosslinking density must reach a certain level.
5) There are also corresponding requirements for product storage. ,
6) The most important point is the control of the entrance of raw materials, which must be approved by everyone and purchased within the allowable scope, and the materials that are suitable for the requirements. These do, I believe this problem is not a problem.